1. Technical Field
This disclosure relates generally to a flow battery system and, more particularly, to a method for operating a flow battery system based on energy costs.
2. Background Information
A typical flow battery system is configured to store and discharge electrical energy. Such a flow battery system, for example, can convert electrical energy generated by a power source into chemical energy, which is stored within a pair of anolyte and catholyte solutions. The flow battery system can later convert the stored chemical energy back into an electrical energy form that can be transferred and used outside of the flow battery system.
Flow battery systems are typically operated at substantially constant and relatively high round trip efficiencies in an effort to maximize net revenue by minimizing operational costs. The term “round trip efficiency” is used herein to describe an efficiency of converting electrical energy to chemical energy, storing the chemical energy, and converting the chemical energy back into electrical energy. The operational costs can be minimized at relatively high round trip efficiencies because the ratio of (i) electrical energy purchased for storage to (ii) electrical energy discharged and sold typically decreases as the round trip efficiency increases. The operation of a flow battery system at such a relatively high round trip efficiency, however, does not account for fluctuations in electrical energy costs. The term “energy costs” or “cost of energy” is used herein to describe a net monetary cost of electrical energy.
Energy costs can be influenced by various factors such as time of day and consumer energy demand. The cost of energy during a typical day, for example, will vary between peak hours (e.g., when consumer demand is at a peak) and non-peak hours (e.g., when consumer demand is at a low).
Energy costs can also be influenced by other factors such as energy surplus. An energy surplus is created when a quantity of electrical energy generated by one or more power sources is greater than the consumer energy demand. The net cost of energy for an operator of a wind turbine can be relatively low or even negative during nighttime hours, for example, when public utilities pay the operator to reduce or cease the wind turbine output to the public power grid when there is an energy surplus thereon.